Candiru

More feared then the piranha, the candiru is actually a tiny subfamily of catfishes that inhabits the murky waters of the Amazon and Orinoco River basins of South America. Typically, candiru feed on blood from other fishes (after attaching themselves to their gills with tooth-like odontodes) but on rare occasions candiru have become lodged in the human urethra. The reasons for this behavior are explored in Bill Schutt's book, Dark Banquet.